The present invention concerns a process for the preparation of bicyclic ketones, which contain blocked hydroxy groups, from corresponding keto acids. All of the conventional processes for the production of carbacyclin intermediate stages, starting with intermediates from the Corey prostaglandin synthesis, especially the .gamma.-lactones, not only proceed by way of many reaction stages (cf. DOS No. 2,912,409 or DOS No. 3,021,895) and yield undesirable by-products, but also demand very strict adherence to the reaction conditions [cf. P. A. Aristoff, J. Org. Chem. 46:1954 (1981)] for the internal Wittig reaction that takes place. According to P. A. Aristoff, hydroxy groups in .gamma.-keto compounds blocked with tetrahydropyranyl (THP), for example, do not withstand more vigorous reaction conditions, such as, for example those described by H. J. Bestmann et al. in "Angew. Chemie" [Applied Chemistry] 92:856 (1980). The primary products are no longer the desired carbacyclin intermediates, but rather compounds of the type of PGA, due to .beta.-elimination of the THP ether in the cyclopentane ring.
It has been discovered that the .gamma.-keto acids, readily accessible from Corey lactones by alkaline opening and Jones oxidation of the .gamma.-hydroxy acid, can be converted with good yields into the .alpha., .beta.-unsaturated ketones by reaction with triphenyl(phenyliminovinylidene)phosphorane. These ketones can be very easily converted into saturated carbacyclin intermediates by hydrogenation or hydride transfer with triethylammonium formate/5% palladium-carbon [cf. R. F. Heck et al., J. Org. Chem. 43:3985 (1978)].